The only known Wilson primes are 5, 13, and 563 (sequence A007540 in OEIS); if any others exist, they must be greater than 5×108.[2] It has been conjectured[3] that there are an infinite number of Wilson primes, and that the number of Wilson primes in an interval [x , y] is about

.

Compare this with Wilson's theorem, which states that every prime p divides (p − 1)! + 1.